Devices are known for soldering thin conducting wires between a microcircuit (chip) and its terminals. Such a wire bonder is described in Italian patent application Nos. 23989 B/85 and 23844 B/83 and in U.S. Pat. No. 4,610,387, and generally comprises a table holding the workpiece, an ultrasonic operating head and a system for feeding the workpieces, which in particular are thin metal strips shaped by photoengraving or punching and which support the microcircuit (chip). The necessary connection wires are bonded between the microcircuits and the ends of said strips.
Commercially available machines are generally of two types, namely a first type with its work table able to move along two horizontal axes X-Y with its operating head in a fixed position, and a second type in which the work table remains stationary during the bonding that is done by a mobile operating head, i.e. one which moves along two orthogonal axes X-Y and is carried by two tables or similar members positioned one on the other and which one is mobile along the X-axis and the other along the Y-axis.
The second type is a development of the first which has a low bonding speed, but because of the way in which is is constructed this second type is also slow and not very accurate. In this respect, in both these processing machines both of the tables have to be moved when process displacements are required in either of the two directions. Due to considerable system inertia and, it is impossible to increase the working rate beyond a certain limit. However, the aspect which affects bonding accuracy the most is that fact that as the two tables are superposed, such that any inaccuracy in the movement of the first table influences the second.
A further important point is that current machines for feeding the strip at a variable pitch require a programmable mechanism devised for this purpose, and comprising a control system, a transmission and a motor.
An object of the present invention is to provide a device for positioning and processing workpieces, and in particular for bonding wires onto electronic components, which is of high operational speed and accuracy, lower constructional cost and shorter maintenance down-times, and which can be programmed to execute operations at differing pitch without external intervention, such as variable-pitch bonding on components of different dimensions.
These and further objects which will be more apparent to a person skilled in the art are attained by a device with movement along two orthogonal axes for positioning and processing workpieces, in particular for bonding wires onto electronic components, characterised in that on said axes, namely the X and Y axes, there are positioned two non-superposed components, the first of which, positioned on the X-axis, comprises means for supporting and clamping the workpiece, whereas the second components, positioned on the Y-axis, carries an operating head for processing purposes.
Said clamping and support means and said operating head are associated with mobile members of the first and second component. These mobile members are driven by linear motors so as to eliminate unwanted weight and working inaccuracy. Said mobile members are preferably bars of polygonal cross-section which are supported by shoes through which compressed air is delivered, i.e. pneumostatic shoes, so as to reduce friction between the surfaces and the ensure excellent rigidity and low inertia. Finally, said workpiece support and clamping elements are also used to drive the workpiece during processing, and it is possible using movement control and programming means to make the work table undergo any required movement pitch, so as to dispense with a normal motor which is an essential item of the feed mechanism of current machines.
A preferred embodiment of the device of the present invention applied to the bonding of wires onto electronic components is described hereinafter by way of example.